gms | German Medical Science

Objectives: Until today, patellar tracking is characterized based on cadaveric biomechanical studies. Although its objective assessment via dynamic magnetic resonance imaging (MRI) has been proposed, normal values are still lacking. The purpose of this study was to provide normal values for physiological patellofemoral tracking in healthy individuals, measured with real-time 3T-Magnetic-Resonance-Imaging (MRI) and to test for reliability of dynamic MRI in measuring patellar tracking.

Methods: Knees of healthy individuals with no history of patellofemoral symptoms were scanned with dynamic, multi-slice gradient-echo MRI-sequences, during repetitive cycles of flexion (40°) and full extension, in open-chain active movement. Within a 30-seconds time frame, three simultaneous, transverse slices were acquired. Dynamic mediolateral patellar translation (dMPT) and dynamic patellar tilt (dPT) were measured on two occasions by two independent examiners. Common radiological parameters were measured in static MRI sequences, and correlations were calculated.

Results and Conclusion: 100 knees (52 male, 48 female, average 26.8±4.5 years, BMI 22.4±2.9) were included. The patients' mean body height was 170±7.7 cm in females and 182±6.4 cm in males. The average diameter of the patellae was 37.9 mm (95% CI 37.2-38.8 mm) in females and 42.4 mm (95% CI 41.1-43.2 mm) in males. In female knees, the patella diameters and intercondylar distances were significantly smaller than in males (p<0.01). Radiological parameters for patellar maltracking were within the normal range.

During the range of motion, mean dMPT was 1.8 mm (95% CI 1.1-2.5 mm) in females and 1.9 mm (95% CI 1.1-2.6 mm) in males. Female knees showed a lateral dPT of 1.7° (95% CI 0.6-2.7°) and male knees presented a medial dPT of -0.4° (95% CI -1.7-0.8°) (p=0.010). No correlations were found between dMPT and body height, patella diameter or intercondylar distance. Intra- and interrater reliability were excellent for dMPT and dPT.

This study establishes normal values for patella tracking, with dynamic MRI being a reliable method. Normal dMPT is 1.8 (1.1-2.5) mm in females and 1.9 (1.1-2.6) mm in males, independent of size or gender. Normal dPT is 1.7 (0.6-2.7)° for females and -0.4 (-1.7-0.8)° for males. These values provide the baseline for evaluation and objectifying pathological patella tracking especially in patients suffer from patella dislocation.